Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and a rotor. The rotor typically includes a rotatable hub having one or more rotor blades attached thereto. A pitch bearing is typically configured operably between the hub and the rotor blade to allow for rotation about a pitch axis. The rotor blades capture kinetic energy of wind using known airfoil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
A power output of the generator increases with wind speed until the wind speed reaches a rated wind speed for the wind turbine. At and above the rated wind speed, the generator operates at a rated power. The rated power is an output power at which the generator can operate with a level of fatigue to turbine components that is predetermined to be acceptable. At wind speeds higher than a certain speed, or at a wind turbulence level that exceeds a predetermined magnitude, typically referred to as a “trip limit” or “monitor set point limit,” wind turbines may be shut down, or the loads may be reduced by regulating the pitch of the rotor blades or braking the rotor, in order to protect wind turbine components against damage.
Variable speed operation of the generator facilitates enhanced capture of energy by the generator when compared to a constant speed operation of the wind turbine generator; however, variable speed operation of the generator produces electricity having varying voltage and/or frequency. More specifically, the frequency of the electricity generated by the variable speed generator is proportional to the speed of rotation of the rotor. Thus, a power converter may be coupled between the generator and the utility grid. The power converter outputs electricity having a fixed voltage and frequency for delivery on the grid.
Wind energy generation and, particularly, reactive power control of the wind turbine power system should take an active part in the stability and quality of the electrical grid. Thus, reactive power compensation of the wind turbine power system is configured to fulfill electrical network demands and maintain a reactive power reserve in order to support grid contingencies. Such objectives may lead to giving priority to reactive power over active power production depending on network conditions. Thus, in a typical wind turbine power system, the turbine controller receives a power command from a farm-level controller that is based on various grid conditions. As such, the power command instructs each wind turbine how much reactive and active power should be generated based on the grid.
In weak grids, the response to a power command can be sluggish. The slow response can be detrimental to functions that require rapid change of power to stabilize the power system (e.g. the drivetrain damper, fast power reduction functions, etc.).
Accordingly, the present disclosure is directed to systems and methods for reducing the delay between a power command and the actual power of wind turbine power systems using a power angle feedforward signal in a phase locked loop (PLL) of the power system.